As well known, an electric power steering apparatus loaded on a vehicle is adapted to apply an assist torque via an electric motor to steering torque applied to a steering shaft by the driver of a vehicle, thereby reducing the operating force on the steering wheel from the driver. In a conventional electric power steering apparatus, a protective relay is provided between a motor driving circuit within a control device of the electric power steering apparatus, and an electric motor, and in a case where a semiconductor switch element used for the electric motor driving circuit has failed, particularly in a case where a semiconductor switch element has failed due to short-circuiting, the protective relay is operated to interrupt the electric motor from the electric motor driving circuit to prevent abnormal behavior of the electric motor (for example, refer to Patent Citation 1).    Patent Citation 1: JP-B-7-96387